Generic milling devices are known from the prior art and are used, for example, in road construction, especially as cold milling machines, stabilisers and/or recyclers, or for the removal of soil material, for example in open cast mining operation as surface miners. Such a milling device features a work roller, the outer surface of which is equipped with a multitude of milling tools, especially chisels. Depending on the application and the normal operation, the work roller can be operated in or against the working direction of the milling device. During the milling operation, the work roller rotates about its axis of rotation and the cutting tools submerging into the ground remove soil to a predetermined milling depth. Such milling equipment is designed either as an attachment parts or, preferably, as self-propelled machines. In order to guarantee an effective and continuous work process, the soil milled off by the work roller is normally transported to a drop point during the milling operation with the help of a conveyor device. From the drop point, the milled material is discharged into a transport container of a transport device, such as a lorry or dump truck. In this process, various arrangements of the milling device and the transport device with respect to the conveyor device are possible. If the milling device is designed as a so-called rear loader, the milled material is discharged from the milling device backward into the transport device. If the conveyor is a side loader, the milled material is transported to the side, and in case of a front loader, the milled material is transferred forward, or in the working direction of the milling device, into the transport device. As soon as the transport container of a transport device is loaded to its maximum fill height, the transport device is removed from the work train and replaced with a transport device with an empty transport container.
During milling operation, the milling device moves in the work direction over the ground to be processed. To achieve a simultaneous milling and discharging of the milled material, the transport device and the milling device must always move in the working or travelling direction at such a distance to one another that the milled material can be transported by the conveyor device into the corresponding transport container of the transport device. Because the transport device normally cannot move forward as slowly as the milling device does and thus the drop point of the conveyor device shifts relative to the transport container in the working direction, the challenge lies in continually monitoring the distance between the transport device and the milling device, adjusting it accordingly and keeping it in a range in which the milled material can still be discharged into the transport container of the transport device reliably and as completely as possible, so as to avoid for example milled material falling off beside the transport container, which poses a considerable accident risk to nearby persons. A common practice is the repeated driving forward and stopping of the transport device relative to the nearly continually moving milling device. Evenly loading over the entire surface of the transport container of the transport device poses a further challenge. This method is explained in greater detail below with a front-loader street milling machine.
If the transport device drives ahead of the milling device, it is difficult for the driver of the transport device to observe the discharging process of the milled material taking place behind his back. Therefore, the following tasks fall upon the driver of the milling device: First, it must be ensured that the milling device mills ground in the desired area and that the milled-off material reaches the transport container of the transport device via the conveyor device as completely as possible. Furthermore, the transport container should be loaded evenly. Moreover, the driver must avoid a collision between the milling device and the transport device driving ahead or following behind. In present practice, coordinating these tasks is solely the responsibility of the operator of the milling device. In addition, he must scan the surroundings for potential dangers, obstacles or curves. All this adds up to place especially high demands on the attentiveness of the operator of the milling device and can quickly lead to errors in the milling and loading operation.
At present, the coordination of the distance between the milling device and the transport device usually occurs in practice via horn signals that are triggered by the operator of the milling device manually and at his own discretion. If the transport device has driven too far forward in the working direction, the milled material no longer reaches the transport container but falls to the ground between the transport device and the milling device. To prompt the driver of the transport device to stop and thus bring the transport container back into the range of the conveyor device, the milling device driver triggers the horn. When the milling device, moving forward with nearly constant speed, has drawn closer to the stopped transport device up to a minimum distance, the milling device driver triggers the horn again to alert the transport device driver to start driving again in order to avoid a collision between the two vehicles. The minimum distance is the distance at which the conveyor device can just still discharge the milled material into the front part of the transport container and at which the milling device does just not yet immediately collide with the transport device. Thereupon, the transport device driver drives forward until the maximum distance between the two vehicles is reached. The maximum distance for the loading process is the distance between both vehicles of the work train in which the milled material is just still discharged into the transport container and does just not yet fall behind the transport container onto the ground. When the maximum distance is reached, the milling device driver again uses a horn signal to instruct the transport device driver to stop the transport device. Relative to one another, the milling device and the transport device therefore oscillate during the loading process between the maximum and minimum distances to one another while moving forward as a whole in the working direction. If the transport container is full, the operator of the milling device gives another corresponding horn signal for departing.
Considering the multitude of tasks that fall upon the operator of the milling device, this activity places especially high demands on his concentration and attentiveness. Moreover, the horn signals can confuse other traffic participants, who might misunderstand the horn signals of the milling device as warning of a danger. At the same time, the driver of the transport device can also be confused and unsettled by the horn signals by other traffic participants. Furthermore, people who live in the area near construction sites, especially in the case of night construction work, can be disturbed by the repeated horn signals.